Description
Potassium-39 has several broad Feshbach resonances that enable the interatomic interaction to be precisely tuned over a wide range of values. In recent years the |1, -1> Feshbach resonance at 33.6 G has been widely used to create 39K BECs because of its convenience, especially in experiments conducted in space.
We have found that the position of the 33.6 G Feshbach resonance can shift by as much as +7.5 G for 39K atoms confined in a 1063.9 nm crossed optical dipole trap (ODT) at temperatures up to around 35 uK and trap depths around 136 uK [1]. This is an order of magnitude larger than the estimated temperature-induced shift. When the atoms are evaporatively cooled to lower temperatures, the shift of the Feshbach resonance approaches zero at zero trap depth. We show that the large observed shift originates from a large differential ac-Stark shift between the incoming pair of 39K atoms and the associated Feshbach molecule in the oscillating electric field of the ODT, which in turn originates from a large dynamic polarizability of the weakly-bound Feshbach molecule. Similarly large shifts occur for the |1, +1>+|1, 0> resonance at 39.9 G, but not for other Feshbach resonances studied.
The dynamic polarizabilities of the Feshbach molecules extracted from the measured shifts are four to seven times larger than the sum of the polarizabilities of the two incoming 39K atoms, which represents the usual polarizability for weakly bound Feshbach molecules. The large polarizabilities are attributed to a near-coincidence between the frequency of the 1063.9 nm ODT laser and the frequency of an electronic transition from the last rovibrational level of the lowest a3Eu+ potential to a rovibrational level of the excited b3Eg+ potential of K2.
| I am the presenting author | Yes |
|---|